provides access to configuration data from a SingleBackend.
If no backend is provided during initalization or if the context
contains an Offline flag that is true, then offline mode
is activated. This may fail, if the offline cache has not been filled
during a previous execution.
Less entities may be available from XBackendEntities,
when operating in offline mode than when operating with an online
SingleBackend.
If offline mode is not invoked, the implementation behaves
like any other BackendAdapter.
